1. Field of the Invention
This invention relates to a display device using a liquid crystal display element for use in electronic equipment such as a mobile phone.
2. Description of the Prior Art
Various electronic instruments such as mobile phones mostly have a display device to give displays convenient for a user's operations.
Mobile phones are being made small in size and light in weight, and are required to be strong in structure. They must have a structure free from damage and failure even when dropped onto a concrete surface from, say, a height of 1 m. Because of this compact, light-weight structure, shock at the time of drop has become less. When a 100 g mobile phone is dropped from a 1-meter height onto a concrete surface, however, a shock as great as about 20 to 30 kgf is exerted, if the shock is expressed as a static load. In the presence of this shock, it goes without saying that the display device must not be damaged or fail.
FIG. 7 is an outside drawing showing a display device portion of a mobile phone to which a conventional display unit has been applied. FIG. 8 is a sectional view taken on line A--A of FIG. 7. FIG. 9 is a sectional view showing a main part of FIG. 8. FIG. 10 is a sectional view taken on line B--B of FIG. 7.
In each of the drawings, the reference numeral 1 designates a case, 2 a display window provided in a surface of the case 1, 3 a sound emission hole formed in correspondence with the position of a speaker (not shown) provided inside the case 1, 4 a liquid crystal display element disposed such that its surface liquid crystal screen is opposed to the display window 2, 5 a transparent plastic coated on an upper surface of an electroluminescence light 6, 6 represents the electroluminescence light as a light source for illuminating the liquid crystal display element 4 from behind via the transparent plastic 5, and 7 an elastic member interposed between a peripheral edge portion of the liquid crystal display element 4 and the case 1 and comprising a rubber sheet, preferably, of silicone rubber. The reference numeral 8 denotes a holder for supporting the liquid crystal display element 4 via the electroluminescence light 6 and the transparent plastic 5, and 9 a rib formed in a peripheral edge portion of the holder 8 and serving to prevent displacement of the liquid crystal display element 4, transparent plastic 5 and electroluminescence light 6 when assembled. The reference numeral 10 signifies a printed circuit board disposed below the holder 8 and bearing electronic parts constituting a drive circuit, etc. for the liquid crystal display element 4, 11 a claw provided in the case 1, and 12 a claw provided in the holder 8 for engagement with the claw 11 of the case 1.
A procedure for assembly of the liquid crystal display element 4 will be described.
The rubber sheet 7 is mounted on the case 1, and then the electroluminescence light 6, transparent plastic 5 and liquid crystal display element 4 are placed in a superposed state on the holder 8. On this occasion, the rib 9 restrains the electroluminescence light 6, transparent plastic 5 and liquid crystal display element 4 so that they are not displaced. In this condition, the holder 8 is pressed against the case 1, and fitted into the case 1. As shown in FIG. 8, the claw 12 of the holder 8 engages the claw 11 of the case 1, whereby the liquid crystal display element 4 can be set in place.
In this state, the rubber sheet 7 is compressed between the liquid crystal display element 4 and the case 1, and the peripheral edge portion of the liquid crystal display element 4 is pressed by the rubber sheet 7. Compressing the rubber sheet 7 in this manner is intended to prevent dust or the like from entering a space between the liquid crystal display element 4 and the display window 2, and to prevent the electroluminescence light 6 from making a sound. In detail, the electroluminescence light 6 uses a power source of a high frequency, and emits light by violent collision of electrons with a light emission layer. Light emission generates a high frequency sound. To prevent this phenomenon, the transparent plastic 5 is stuck onto the electroluminescence light 6. To press the transparent plastic 5 firmly against the electroluminescence light 6, thereby preventing sounding, the rubber sheet 7 is compressed as mentioned above.
According to the conventional display device constructed in the above manner, the peripheral edge portion of the liquid crystal display element 4 is pressed by the rubber sheet 7. This poses no problems to display in normal times. When stress P is exerted at a position indicated by an arrow in FIG. 9, however, this stress acts directly on the liquid crystal display element 4 via the rubber sheet 7. As a result, a rainbow pattern occurs in a display around the site of stress in the liquid crystal display element 4. This phenomenon is ascribable, as is well known, to the fact that the gap of the liquid crystal sealed-in portion shrinks owing to the stress.
Furthermore, when shock is imposed on the position of the arrow by a drop or the like, the shock is conveyed to the liquid crystal display element 4, which may be damaged thereby.